The present invention is in the field of optical reflectors and more particularly in the field of reflector lamps.
One general type of reflector lamp comprises a concave reflector having a parabolic contour with respect to a focal point, so as to reflect frontwardly and along the lamp axis light emitted by a light source located at and near the focal point. The cross section of the reflector, perpendicular to the lamp axis, usually is circular with the diameter thereof varying with the distance from the focal point. Additionally, a cone of light rays, originating from the light source, pass, unreflected, through the front of the reflector; the angle of this cone of rays being determined and defined by the front rim of the reflector. The more widely divergent light rays of the cone of rays, that is, the rays passing relatively nearer to the rim of the reflector, have such a large sideways component of direction so as to fall outside of the desired light pattern and therefore are wasted.
The wasted, divergent light can be reduced, and the optical efficiency improved, by making the reflector deeper, that is longer, so that relatively more of the light is reflected in the desired direction and the cone of nonreflected light is narrowed. However, there are practical limitations on increasing the depth of the reflector, such as cost, weight and awkwardness of use. Also, with a given maximum diameter as the reflector is made deeper, the focal point moves closer to the rear surface, which complicates positioning of the light source and if the light source is a filament there is accelerated blackening of the nearby rear area of the reflector due to evaporation of the filament material (usually tungsten). This accelerated blackening can be alleviated by providing a concave recess at the rear portion of the reflector but has the drawback of reducing optical efficiency.
As disclosed in the cross-referenced application Ser. Nos. 349,334 and 352,741, reflectors have been designed which substantially eliminate the wasted, divergent light and accelerated blackening of the reflector rear area described heretofore. However, such reflectors produce an asymmetrical beam pattern due to the long, slender configuration of the lamp filament. That is, the beam pattern is not circumferentially uniform about the lamp axis. One means of providing a more symmetrical beam pattern is to place a diffusing lens over the lamp. Optical correction of the beam pattern through use of a diffusing lens, however, has several disadvantages including large variations in lens thickness resulting in a more costly and difficult lens to manufacture. Additionally a diffusion lens spreads the beam pattern in an undesirable radial direction. That is, the lens broadens the beam pattern creating undesirable and wasted divergent light which is counter to the advancement over the prior art as disclosed in the cross-referenced applications.